Theoretical Model for Predicting the Transient Response of the Mixture-Vapor Transition Point in Horizontal Evaporating Flow

1968 ◽  
Vol 90 (1) ◽  
pp. 165-174 ◽  
Author(s):  
G. L. Wedekind ◽  
W. F. Stoecker
Keyword(s):  
Theoretical Model ◽  
Transient Response ◽  
Transition Point ◽  
Transient Flow ◽  
Horizontal Tube ◽  
Phase Region ◽  
Two Phase ◽  
Instantaneous Position ◽  
Complete Vaporization ◽  
The Mean

A horizontal tube evaporator in which complete vaporization takes place can be divided into two distinct regions—a two-phase region and a superheat region. The mixture-vapor transition point refers to the boundary between these two regions. Experimental evidence is presented which indicates that, during steady as well as transient flow conditions, the motion of the mixture-vapor transition point is of an oscillatory nature. Furthermore, the amplitudes of the oscillations appear to be sufficiently random to preclude the possibility of predicting an instantaneous position. Therefore, a theoretical model is proposed for predicting the transient response of the mean position of the transition point. Experimental validation of the theoretical model is reasonably well established.

An Experimental Investigation Into the Oscillatory Motion of the Mixture-Vapor Transition Point in Horizontal Evaporating Flow

1971 ◽  
Vol 93 (1) ◽  
pp. 47-54 ◽  
Author(s):  
G. L. Wedekind
Keyword(s):  
Transition Point ◽  
Transient Flow ◽  
Horizontal Tube ◽  
Rayleigh Distribution ◽  
Phase Region ◽  
Statistical Characteristics ◽  
Two Phase ◽  
Physical Mechanisms ◽  
Complete Vaporization ◽  
Flow Quality

A horizontal tube evaporator in which complete vaporization takes place can be divided into two distinct regions: a two-phase region and a super heat region. The mixture-vapor transition point refers to the boundary between these two regions. Experimental evidence indicates that, during steady as well as transient flow conditions, the motion of the mixture-vapor transition point is of an oscillatory nature. This study is concerned with the statistical characteristics of these oscillations, the physical mechanisms causing them, and the influence of various evaporator parameters. Experimental data are presented which indicate that the statistical characteristics of the transition point oscillations can be described by a transformed Rayleigh distribution, and that the inlet flow quality and evaporator heat flux have a considerable influence on this distribution.

Theoretical Model of the Mixture-Vapor Transition Point Oscillations Associated With Two-Phase Evaporating Flow Instabilities

1974 ◽  
Vol 96 (2) ◽  
pp. 138-144 ◽  
Author(s):  
G. L. Wedekind ◽  
B. T. Beck
Keyword(s):  
Theoretical Model ◽  
Transition Point ◽  
Horizontal Tube ◽  
Rayleigh Distribution ◽  
Flow Instabilities ◽  
Statistical Characteristics ◽  
Two Phase ◽  
Proposed Model ◽  
Complete Vaporization ◽  
Liquid Film Dryout

A horizontal tube evaporator in which complete vaporization takes place can be divided into three distinct regions—a subcooled, a two-phase, and a superheat region. The mixture-vapor transition point corresponds to the liquid film dryout point, and when entrainment is negligible, it represents the boundary between the two-phase and superheat regions. Experimental evidence indicates that during what is conventionally accepted as steady flow conditions, the motion of the mixture-vapor transition point is of an oscillatory nature. Furthermore, not only are the oscillations random, but their statistical characteristics can be represented by a modified Rayleigh distribution. This paper presents the formulation of a theoretical model which incorporates various deterministic mechanisms, while at the same time includes the existence of a random phenomenon. The model has the capability of predicting the influence of evaporator heat flux and inlet flow quality on the statistical characteristics of the transition point oscillations. Perhaps, the most significant potential of the proposed model is that it represents a first step toward the formulation of some of the fundamental mechanisms associated with two-phase evaporating flow instabilities on a statistical basis; a basis which appears to be consistent with many of the experimental observations currently available.

An Investigation Into the Effect of Subcooled Liquid Inertia on Flow-Change-Induced Transient Flow Surges in Horizontal Condensing Flow Systems

2005 ◽  
Vol 127 (11) ◽  
pp. 1280-1284 ◽  
Author(s):  
C. J. Kobus
Keyword(s):  
Flow Rate ◽  
Large Scale ◽  
Transient Flow ◽  
Phase Region ◽  
Complex Nature ◽  
Vapor Flow ◽  
Two Phase ◽  
Subcooled Liquid ◽  
Flow Systems ◽  
Final Steady State

The objective of this research is to investigate large-scale transient flow surges of the condensate leaving in-tube condensing flow systems because of perturbations in the inlet vapor flow rate, and the influence of the subcooled liquid inertia of the condensate on these transient responses. Small changes in the inlet vapor flow rate momentarily cause large transient flow surges in the outlet liquid flow rate. Condensate inertia is seen to destabilize the system into an underdamped behavior where the flow rate can overshoot the final steady-state position several times. A one-dimensional, two-fluid, distributed parameter system mean void fraction (SMVF) model of the time-dependent distribution of liquid and vapor within the two-phase region is developed for predicting these transient characteristics, which it is seen to do quite well, especially when consideration is given to the complex nature of the problem.

NUCLEATION AND METASTABILITY IN THE CO2 SYSTEM

2003 ◽  
Vol 14 (01) ◽  
pp. 81-94 ◽  
Author(s):  
DIETER W. HEERMANN ◽  
TING WANG ◽  
WEI-DER LEE
Keyword(s):  
Atomistic Simulation ◽  
Distribution Density ◽  
Mean Field ◽  
Coexistence Curve ◽  
Phase Region ◽  
Density Fluctuations ◽  
Two Phase ◽  
Droplet Distribution ◽  
The Mean ◽  
Observation Period

We have investigated metastability and nucleation in the CO 2 system. To facilitate comparison with experiment and analytical theories, we have also calculated the coexistence curve. The metastability properties were computed using three methods to calculate the compressibility: droplet distribution, density fluctuations, and structure factor. These provide three measures for the time-dependent compressibility. If the compressibility showed a window in which it was quasi time-independent, for the observation period we categorized the quench to lead into a metastable state. Our fully atomistic simulation shows that the metastable region is extremely small. Already, very shallow quenches into the two-phase region have given rise to nonclassical behavior. The calculated pseudo spinodal is located far from the mean field expectation.

The dynamics of strong turbulence at free surfaces. Part 2. Free-surface boundary conditions

2001 ◽  
Vol 449 ◽  
pp. 255-290 ◽  
Author(s):  
M. BROCCHINI ◽  
D. H. PEREGRINE
Keyword(s):  
Free Surface ◽  
Boundary Conditions ◽  
Equations Of Motion ◽  
Phase Region ◽  
The Body ◽  
Breaking Wave ◽  
Surface Boundary ◽  
Two Phase ◽  
Strong Turbulence ◽  
The Mean

Strong turbulence at a water–air free surface can lead to splashing and a disconnected surface as in a breaking wave. Averaging to obtain boundary conditions for such flows first requires equations of motion for the two-phase region. These are derived using an integral method, then averaged conservation equations for mass and momentum are obtained along with an equation for the turbulent kinetic energy in which extra work terms appear. These extra terms include both the mean pressure and the mean rate of strain and have similarities to those for a compressible fluid. Boundary conditions appropriate for use with averaged equations in the body of the water are obtained by integrating across the two-phase surface layer.A number of ‘new’ terms arise for which closure expressions must be found for practical use. Our knowledge of the properties of strong turbulence at a free surface is insufficient to make such closures. However, preliminary discussions are given for two simplified cases in order to stimulate further experimental and theoretical studies.Much of the turbulence in a spilling breaker originates from its foot where turbulent water meets undisturbed water. A discussion of averaging at the foot of a breaker gives parameters that may serve to measure the ‘strength’ of a breaker.

Solution Properties and Phase Behavior of Ammonium Hexylene Octyl Succinate in Water and Water-Oil System

1970 ◽  
Vol 3 (1) ◽  
Author(s):  
Md. Hamidul Kabir ◽  
Ravshan Makhkamov ◽  
Shaila Kabir
Keyword(s):  
Critical Micelle Concentration ◽  
Phase Behavior ◽  
Liquid Crystalline ◽  
Carbon Number ◽  
Phase Region ◽  
Solution Properties ◽  
Middle Phase ◽  
Two Phase ◽  
Lamellar Liquid Crystal ◽  
Drug Ingredient

The solution properties and phase behavior of ammonium hexylene octyl succinate (HOS) was investigated in water and water-oil system. The critical micelle concentration (CMC) of HOS is lower than that of anionic surfactants having same carbon number in the lipophilic part. The phase diagrams of a water/ HOS system and water/ HOS/ C10EO8/ dodecane system were also constructed. Above critical micelle concentration, the surfactant forms a normal micellar solution (Wm) at a low surfactant concentration whereas a lamellar liquid crystalline phase (La) dominates over a wide region through the formation of a two-phase region (La+W) in the binary system. The lamellar phase is arranged in the form of a biocompatible vesicle which is very significant for the drug delivery system. The surfactant tends to be hydrophilic when it is mixed with C10EO8 and a middle-phase microemulsion (D) is appeared in the water-surfactant-dodecane system where both the water and oil soluble drug ingredient can be incorporated in the form of a dispersion. Hence, mixing can tune the hydrophile-lipophile properties of the surfactant. Key words: Ammonium hexylene octyl succinate, mixed surfactant, lamellar liquid crystal, middle-phase microemulsion. Dhaka Univ. J. Pharm. Sci. Vol.3(1-2) 2004 The full text is of this article is available at the Dhaka Univ. J. Pharm. Sci. website

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